Wattmeters of various types have been employed in the past to indicate the amount of power passing a particular location in a circuit by measuring the voltage at that location, and the current passing that location. When measuring power in alternating current circuits, it is necessary to take into consideration the relative phase relationship of the current and voltage, such that only the in-phase components are multiplied to determine the number of watts of power passing a particular location in a circuit.
Mechanical watt-hour meters have typically been employed in the past by power companies wishing to measure the amount of alternating current power that is used at a customer's location. With the advent of solid state electronic devices, watt and watt-hour meters utilizing such solid state devices have been disclosed. Many of these disclosed watt and watt-hour meters employing solid state devices utilize pulse circuit techniques. Such watt and watt-hour meters are disclosed in U.S. Pat. Nos. 3,500,200--Woodhead; 3,517,311--Wasielewski et al; 3,780,273--Turrell; and 3,953,795--Brunner et al. Still other patents showing solid state watt or watt-hour meters utilizing solid state devices employing pulse techniques are U.S. Pat. Nos. 3,976,942--Mayfield and 3,959,724--Chana et al.
U.S. Pat. No. 4,437,059--Hauptmann is similar to the previously mentioned patents in disclosing a solid state wattmeter utilizing pulse techniques. However, the disclosure of the Hauptmann patent is directed to features of the magnetic coupling to the conductors in which the current flow is to be measured, and to the use of photoelectric devices for coupling purposes.
It is an object of the present invention to provide a watt transducer for AC power measurement utilizing an integrated circuit analog multiplier providing four quadrant multiplication which receives two alternating current inputs, one proportional to the current and the other to the voltage associated with the alternating current power to be measured.
It is a further object of the present invention to provide an alternating current watt transducer wherein the in-phase components of AC signals which are proportional to the AC voltage and AC current associated with the power to be measured, are multiplied by each other, so as to provide an alternating current output signal proportional to the AC power to be measured.
It is a still further object of the present invention, when applied to multi-phase applications, to add signals representing the power in each of the phases to provide a signal representative of the total power being measured in the multi-phase circuit. Further, without regard to whether the watt transducer of this invention is utilized for single phase or multi-phase power measurements, a signal conversion circuit is provided to develop from an alternating current signal representative of the total power being measured, a constant-current DC output which is also indicative of the total power being measured.